In accordance with the principles of the present invention, in addition to conventional use of
frequency division multiplexed upper and lower side bands, the spectral area occupied by the analog host will be utilized by applying a one-dimensional modulation, e.g.,
pulse amplitude modulation (PAM) as opposed to the conventional use of a two-dimensional modulation, e.g.,
quadrature amplitude modulation (
QAM). Furthermore, the analog and digital information within the analog host bandwidth may be combined in quadrature to keep the signals orthogonal. Thus, should one
side band under the analog carrier be deteriorated or obliterated by
adjacent channel interference, the other
side band under the analog carrier can still provide useful data and hence better
digital audio codec performance. By transmitting one or two
digital data streams asymmetrically with respect to the
center frequency, particular digital side bands can be rendered useless as environmental conditions warrant (e.g., as they become detrimentally affected by
adjacent channel interference), reducing bandwidth capacity but not affecting the quality of the received
digital data transmitted in any of the remaining digital
side band regions.